The background to the invention will be described in the context of catalytic reforming processes, although the invention is not so limited and has application to a variety of industrial processes in which monitoring of plant equipment, including vessels, chambers and fluid conduits, is beneficial. It will be apparent that the invention is particularly useful in industrial applications which use large vessels or chambers for containing fluids and/or feedstocks during reaction processes.
Catalytic reforming processes are used to increase the octane ratings of petroleum refinery feedstocks to form into high octane liquid products, and are utilised during the generation of the majority of the world's gasoline. A number of catalytic reforming processes have been development since 1940s, all of which use platinum and/or rhenium catalysts. Examples include the proprietary Platforming process developed by Universal Oil Products; the Rheniforming process proprietary to Chevron Oil Company; the Powerforming process proprietary to ExxonMobil; and the proprietary Ultraforming process of BP. A typical catalytic reforming process takes place in a large cylindrical vessel of approximately 2 to 4 meters in diameter, and is a continuous process which takes place at a temperature of around 400° C. to 600° C. FIG. 1 shows a typical vessel 10, having a cylindrical outer wall 12, oriented vertically on a concrete support 14 which surrounds a lower part 16 of the vessel.
In order to prevent heat losses and to preserve the external wall of the vessel 10, a stainless steel liner is fitted on the interior wall of the vessel, with a layer of insulating material between the inner and outer walls. During normal operation, the typical temperature of the outer wall is around 180° C. Over its lifetime, the interior stainless steel liner can be damaged, which may allow leakage of the hot reactants into the insulation layer. This exposes the outer wall to high temperatures, and the inside surface of the outer wall to hydrogen. “Hot spots” develop on the vessel surface. In the presence of the hot spot, High Temperature Hydrogen Attack (HTHA) can lead to severe local weakening of the structure. Conventionally, hot spots have been detected through a change in colour of heat-sensitive paint applied to the outer surface of the vessel. Typically, this will change colour at temperatures above 200° C. and provide a visual indication 18 of a hot spot.
For many industrial installations, visual inspection by the use of heat sensitive paints is inadequate for the monitoring of the condition of the vessel. Firstly, the heat sensitive paint does not provide any quantitative data about the maximum temperature that has been reached. Secondly, the geometry of the installation in the vessel often means that visual inspection is not possible. For example, many catalytic reforming process vessels have a concrete support which obscures visual inspection of the vessel, of the type shown in FIG. 1.
More recently, it has been proposed to provide temperature monitoring of catalytic reforming process vessels by using fibre optic Distributed Temperature Sensor (DTS) systems. An example of a distributed temperature sensor is described in GB 2239310. Another example of a suitable DTS system is the applicant's proprietary system marketed under the ULTIMA trade mark.
In a typical application of a fibre optic monitoring system, the fibre optic is wrapped around the outer surface of a vessel in a continuous length, to provide a suitable surface distribution for monitoring the temperature of the vessel. However, to date this approach has been limited to the exposed parts of the vessel; the surface of the vessel which is beneath structural elements such as the concrete support 14 is unable to be monitored due to installation difficulties.
Other disadvantages of the previously proposed systems are apparent. In particular, installing the fibre optic on the surface of the vessel by the conventional methods can only be performed during process shutdowns. The installation method is also time consuming and labour intensive. Conventional installation methods also have an unacceptable risk of mechanical damage to the cable. Furthermore, this type of installation is not well disposed to removal and replacement, which may be necessary to allow inspection and repair of the vessel, or to replace a malfunctioning or damaged fibre optic length.
It is amongst the aims and objects of the invention to provide a fibre optic monitoring installation, apparatus and/or method which overcomes one or more drawbacks and deficiencies of the presently available apparatus and methods.
Additional aims and objects of the invention will become apparent from the following description.